Python cheat sheet
==================

Use the adapted type
--------------------

A dict **is not** an ordered type. If you need an ordered dict, use a more
advanced collection type like the ordered dict::

  >>> from collections import OrderedDict
  >>> d = OrderedDict({'banana': 3, 'apple': 4, 'pear': 1, 'orange': 2})
  >>> d
  OrderedDict([('orange', 2), ('apple', 4), ('banana', 3), ('pear', 1)])
  >>>


Careful about Mutable types and non-mutable types
---------------------------------------------------

A set is immutable, whereas a list is mutable::

    >>> s = set([1,2])
    >>> l = [1,2]
    >>> l.append(3)
    >>> list(l)
    [1, 2, 3]
    >>> s.append(3)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    AttributeError: 'set' object has no attribute 'append'
    >>>

A string is immutable. If you want to modify it, build another string:

    >>> s = "hello"
    >>> s.replace('ll', 'bb')
    'hebbo'
    >>> s+"you"
    'helloyou'
    >>> s
    'hello'

Base type are objects
---------------------


It means that in python, classes are types (let's understand it like that at first glance)

    >>> a = 2
    >>> isinstance(a, int)
    True
    >>> s = "a"
    >>> dir(s)
    ['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__',
    '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__',
    (...)
    '__init__', '__iter__', '__le__', '__len__', '__lt__', ]

`s` has methods. It's an objects. The type of s is the class `int`.

    >>> d = {'banana': 3, 'apple': 4, 'pear': 1, 'orange': 2}
    >>> isinstance(d, dict)
    True
    >>>

.. important:: **But** a base type doesn't have attributes.

>>> a = 2
>>> a.a = 5
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'int' object has no attribute 'a'
>>>

If you want attributes in types you have to inherit from the base types::

  >>> class A(int): pass
  ...
  >>> a = A()
  >>> a.a = 5
  >>>